15 Operating-System Interface
The Scheme standard provides a simple mechanism for reading and writing
files: file ports.  MIT/GNU Scheme provides additional tools for
dealing with other aspects of the operating system:
     
- Pathnames are a reasonably operating-system independent tool for
manipulating the component parts of file names.  This can be useful for
implementing defaulting of file name components. 
- Control over the current working directory: the place in the file
system from which relative file names are interpreted. 
- Procedures that rename, copy, delete, and test for the existence of
files.  Also, procedures that return detailed information about a
particular file, such as its type (directory, link, etc.) or length.
     
- Procedures for reading the contents of a directory.
     
- Procedures for obtaining times in various formats, converting between
the formats, and generating human-readable time strings.
     
- Procedures to run other programs as subprocesses of Scheme, to read
their output, and write input to them.
     
- A means to determine the operating system Scheme is running under.